Treatment of diseases and ailments of the body often benefit from short- or long-term infusion of therapeutic compositions. While such therapeutic compositions may be administered extracorporeally, e.g., via transcutaneous injection, many patients benefit from the consistent and repeatable dosage provided by an implantable infusion device. Such devices may employ a reservoir for storing an infusible therapeutic composition and a pumping mechanism coupled to the reservoir for discharging the infusible fluid through an outlet of the device. The discharge outlet is typically connected to flexible medical tubing, e.g., a catheter, leading to a targeted delivery site within the patient. The infusion device may further include electronics to control delivery of the therapeutic composition to the patient in accordance with a prescribed schedule.
Implantable infusion devices are typically implanted subcutaneously, e.g., in the chest or abdominal cavity. The device reservoir may be accessible via a self-sealing, needle-penetrable septum. Such devices are typically implanted so that the septum is located generally directly beneath the skin. The septum provides a fluid passageway that permits the reservoir to be refilled periodically via a transcutaneous injection. Accordingly, the pump reservoir can be filled or refilled without requiring surgical removal from the patient's body, and further without requiring any other significant surgical procedure.
During initial filling or refilling of the reservoir, gas bubbles or gas dissolved or entrained in the infusible therapeutic composition may be introduced into the reservoir. Formation or introduction of gas bubbles in the reservoir can potentially lead to problems with the pumping mechanism that can result in inaccurate delivery of the therapeutic composition or pump failure. For many infusion devices, it is recommended to vent or aspirate the reservoir prior to refilling to remove air trapped in the reservoir. In some case, it is also recommended to degas the therapeutic composition prior to introducing the composition into the reservoir. Such processes can be time consuming and may not be fully effective, due in part to faulty technique.
While air bubbles can cause problems with many pumping mechanisms, with piston pumps air bubbles tend to cause inaccurate delivery of fluid due to the volume occupied by the air. Further many implantable infusion devices employing piston pumps include valves upstream or downstream of the piston. Air in the system may result in inoperability of the system due to inability to generate sufficient pressure to draw or force air through the valves or may require prolonged amounts of time to clear the air prior to resuming fully functional operation.